The present disclosure relates to an apparatus for controlling inverter, and more particularly to an apparatus for controlling an inverter capable of detecting a rotation angle of a load when controlling the load using a voltage/frequency control method, and controlling the load in response to the detected rotation angle.
An inverter is an electronic circuit for converting alternating current (AC) to direct current (DC), switching the converted DC voltage using switching elements such as transistors and IGBTs (Insulated Gate Bipolar Transistors), converting again to AC voltage, supplying the converted AC voltage to a load and driving the load. The inverter may adjust a switching gap of the switching elements to enable a user to drive the load using a desired frequency.
The inverter may be classified into a converter unit, an inverter unit and a controller according to respective operations.
The converter unit may include a three-phase rectifying circuit and a smoothing circuit, where a three-phase AC voltage is rectified by the three-phase rectifying circuit for conversion into a pulsating voltage, and the pulsating voltage is smoothed by the smoothing circuit to be converted to a DC voltage having a relatively low amount (small) of residual pulsation, or ripple.
The inverter unit serves to switch the DC voltage converted by the converter unit using switching elements (e.g., the transistors and IGBTs) and convert to an AC voltage. The inverter unit then supplies the converted AC voltage to a load and drives the load. A frequency of the AC voltage converted by the inverter unit may be adjusted in response to a switching speed of the switching element.
The controller that includes an arithmetic circuit, a detection circuit and a driving circuit may perform a switching control of the inverter unit, a voltage control of the converter unit and various operations for protection functionality.
The inverter unit employs a conventional voltage/frequency control method in controlling a load drive without detecting a driving speed of a load using a speed detection sensor such as an encoder and the like. The voltage/frequency control method may adjust a voltage supplied to a load to controllably drive the load using a frequency desired by a user.
In case a momentary power failure occurs in a state where an inverter drives an electric motor using the voltage/frequency control method, the electric motor is operated on a free run state. In case the power is supplied to allow an inverter to drive the electric motor again using the voltage/frequency control method in a state where the electric motor is driven on the free run state, the inverter may supply to the electric motor a voltage that is not consistent with a current rotation speed of the electric motor, whereby an over-current may flow to the inverter to damage the electric motor.
Accordingly, there is a need of searching for a speed of the electric motor for protection of the electric motor in case the momentary power failure occurs while the electric motor is driven by the voltage/frequency control method.